What is the difference between Mie scattering and Fraunhofer diffraction ?

What is the difference between Mie scattering and Fraunhofer diffraction ?

Strictly derived from Maxwell's electromagnetic theory, Mie scattering theory is a theory describing the scattering of light by a uniform sphere with a smooth surface, taking into account the optical properties (refractive index and absorption coefficient) of the scatterer (particle). The Fraunhofer diffraction theory is derived from the original wave theory of light, which is an approximation of Maxwell's theory in small angles, generally valid within 5 °. The diffraction theory does not consider the optical properties of scattered particles. If the instrument only measures the scattered light distribution within 5° or coarse particles larger than 3 microns, then the diffraction theory can be applied, otherwise the Mie theory should be applied. If the optical properties of the scatterers are difficult to measure, then the measurement of particles up to 0.1μm is preferred by diffraction theory.

What are the advantages and disadvantages of semiconductor laser?

Semiconductor Laser, also known as Laser Diode (LD), is one of the latest achievements of semiconductor physics development in the 1980s. The advantages of semiconductor laser are small size, light weight, good reliability, long service life, low power. In addition, the semiconductor laser uses low voltage constant current power supply mode, the power failure rate is low, the use of safety, low maintenance cost. At present, the number of use of semiconductor lasers ranks first among all lasers, some important application fields, used in the past other lasers, have been gradually replaced by semiconductor lasers.

The laser performance of early semiconductor laser is greatly affected by temperature, and the divergence Angle of the beam is also large (generally between several degrees and 20 degrees), so it is poor in directivity, monochromatic property and coherence. But with the rapid development of science and technology, the performance of semiconductor laser has reached a very high level, and the beam quality has also been greatly improved.

When the semiconductor laser is used as the light source of the laser particle size meter, constant temperature measures must be taken to ensure the stability of the output power, so the circuit is more complex.